Conventional tubular ozonisers have an outer electrode preferably consisting of high-grade steel and an inner electrode in the form of a conducting coating deposited on the inner wall of a glass tube. The annular space between the inner wall of the high-grade steel tube and the outer wall of the glass tube forms the discharge gap.
The (necessary) cooling of the outer electrode presents no difficulties of any kind. The situation is different with respect to the cooling of the inner electrode, which is indispensable for increasing the power density. The direct impacting of the inner electrode or of the glass tube with a cooling liquid as is, for example, proposed in German Offenlegungsschrift No. 2,537,124 involves the risk that, in the event of a fracture of the dielectric tube, cooling liquid gets into the discharge chamber and causes consequential damage there. It is therefore necessary to design the inner cooling circuit using pressure-resistant and tough materials. For this purpose, the high-grade steel material, for example, which has proved its value in the outer cooling circuit, is an obvious choice.
Hitherto it has been assumed that a dielectric had to be mounted directly as a close fit on such a high-grade steel tube, since under no circumstances must an air gap be left between the dielectric and the inner electrode (steel tube). An electric discharge would otherwise form in the air gap, which would mean energy loss and that the heat transfer would be poor (with an air gap of 0.5 mm, the internal cooling would already be pointless because of the poor heat conduction).